Organic electroluminescent device having a diffraction grating for enhancing light extraction efficiency

Abstract

An organic electroluminescent device is provided, which includes an emission portion comprising a first electrode and a second electrode and an organic layer sandwiched between the first and second electrodes, and a diffraction grating disposed neighboring on the emission portion, the diffraction grating having first regions and a second region, the first regions comprising a plurality of pair of recessed and projected portions, the plurality of pair of recessed and projected portions being periodically arranged and provided with a primitive translation vector of a direction, the second region comprising an aggregate of the first regions and located parallel with an emission surface of the organic electroluminescent device.

1. An organic electroluminescent device, comprising:
 an emission portion comprising a first electrode and a second electrode and an organic layer sandwiched between the first and second electrodes; and 
 a diffraction grating disposed neighboring on the emission portion, the diffraction grating being constituted by a base material layer having recessed and projected portions on a surface thereof, and a medium deposited on the base material layer to bury the recessed portions of the recessed and projected portions, the diffraction grating having first regions and second regions, each of the first regions being a portion of a planar section of the base material layer and comprising a group of the recessed and projected portions, the second region being a portion of the planar section of the base material layer which includes the plurality of the first regions wherein the diffraction grating has different periodic axes over an entire region of the emission portion, and consisting of an aggregate of a plurality of the first regions, there being at least 5 pairs of recessed and projected portions within each of the first regions being arranged with two-dimensional periodicity in a same direction parallel with the substrate and with a primitive translation vector of a predetermined direction, the predetermined direction of the primitive translation vector of the recessed and projected portions of each of the first regions differing from each other, and the medium being a different material from that of a neighboring transparent electrode material. 
 
     
     
       2. The organic electroluminescent device according to  claim 1 , wherein a plurality of pairs of recessed and projected portions of the first regions are formed in two-dimensional periodicity, and the number of the pairs of recessed and projected portions, in the direction of a primitive translation vector, is confined within the range of 5 to 5000. 
     
     
       3. The organic electroluminescent device according to  claim 2 , wherein the number of the pairs of recessed and projected portions of the first region is 10 or more. 
     
     
       4. The organic electroluminescent device according to  claim 2 , wherein the number of the pairs of recessed and projected portions in the first region is not more than 1000. 
     
     
       5. The organic electroluminescent device according to  claim 1 , wherein a plurality of pairs of recessed and projected portions of the first region are provided with a periodicity in the direction of a primitive translation vector, and a length of the periodicity is confined within the range of 0.1 μm to 5 μm, and a height of the projected portions is confined within the range of 50 nm to 20 μm. 
     
     
       6. The organic electroluminescent device according to  claim 1 , wherein there are a plurality of intervals between respective recessed portions and projected portions and each of the intervals is within the range of 80% to 120% of an average interval of the plurality of intervals. 
     
     
       7. The organic electroluminescent device according to  claim 1 , wherein there are a plurality of heights of respective projected portions in the first region and each of the heights is within the range of 80% to 120% of an average height of the plurality of heights. 
     
     
       8. The organic electroluminescent device according to  claim 1 , wherein the organic electroluminescent device comprises a substrate and the diffraction grating is positioned between the substrate and the emission portion. 
     
     
       9. The organic electroluminescent device according to  claim 1 , wherein the organic electroluminescent device comprises a substrate and the diffraction grating is positioned via the emission portion above the substrate. 
     
     
       10. The organic electroluminescent device according to  claim 1 , wherein the base material layer has a refractive index which is different from that of the medium.